A torsional damper for absorbing a torsional vibration (a vibration in a rotational direction) generated in a crank shaft of an internal combustion engine of a vehicle in accordance with a rotation is provided with a structure in which a metal annular mass is coaxially and elastically connected to an outer periphery of a metal hub fixed to a crank shaft via an annular rubber, and lowers the torsional vibration in a specific rotating speed range on the basis of a dynamic vibration absorbing effect caused by a resonance in a torsional direction. The torsional damper includes a so-called fitting type torsional damper, and this type of torsional damper is manufactured by pressure inserting and fitting a rubber formed in an annular shape into a portion between opposing peripheral surfaces of the hub and the annular mass from one side in an axial direction.
Since the fitting type torsional damper is structured such that the hub, the annular rubber and the annular mass are connected to each other only on the basis of a frictional resistance caused by a compression reaction force of the rubber at a time of being pressure inserted, there is a risk that a slip in a circumferential direction is generated between the fitting surfaces of the hub or the annular mass and the annular rubber at a time when an input torque is increased. Accordingly, in order to prevent the slip mentioned above from being generated, it is necessary to improve a sliding torque between the hub, the annular rubber and the annular mass.
As a typical conventional art for improving the sliding torque between the hub, the annular rubber and the annular mass in the fitting type torsional damper, Japanese Patent Unexamined Patent Publication No. 2001-27287 describes a structure in which a silane coupling agent is applied to the opposing peripheral surfaces between the hub and the annular mass or the annular rubber at a time of pressure inserting the annular rubber to the portion between the opposing peripheral surfaces of the hub and the annular mass arranged in the outer peripheral side of the hub. In other words, the silane coupling agent interposed in the fitting surface between the hub and the annular mass or the annular rubber achieves a significant effect for increasing the sliding torque.
However, in accordance with the conventional art mentioned above, since the silane coupling agent dries quickly, the silane coupling agent applied to the opposing surfaces of the hub and the annular mass, or the annular rubber pressure fitted to the portion between the opposing surfaces dries in a short time. Accordingly, there is pointed out a problem that a pressure inserting load is increased on the basis of an increase of a frictional resistance with the hub and the annular mass, due to generation of an adhesive property of the silane coupling agent at a time of pressure inserting the annular rubber. Further, a swelling deformation on the basis of an internal stress is generated in the annular rubber during a pressure inserting process, by the increase of the pressure inserting load, whereby a durability of the annular rubber is lowered, and a accuracy of oscillation in an axial direction of the annular mass is deteriorated, so that there is a risk that an oscillating motion of the annular mass during the rotation is increased.
The present invention is made by taking the problem mentioned above into consideration, and a technical object of the present invention is to increase a sliding torque between a hub, an annular rubber and an annular mass without increasing a pressure inserting load at a time of pressure inserting the annular rubber to a portion between opposing peripheral surfaces of the hub and the annular mass.